?-lactams, like penicillin and the cephalosporins, are the most widely prescribed class of antibiotics in clinical use today. In response to their extensive use and misuse, resistance has developed and is now one of the most pressing public health crises of the 21st century. Many resistant bacteria express ?-lactamase enzymes. These enzymes hydrolyze the defining lactam ring, rendering them inactive toward their original target, the transpeptidases that crosslink the bacterial cell wall. ?-lactamases are categorized into four, distinct classes (A, B, C, and D) based on sequence similarity and mechanism of action. In an effort to overcome resistance, inhibitors have been developed to block the activity of these enzymes. Of particular concern are the class D ?-lactamases, or oxacillinases, which are not typically inhibited by the classic ?-lactam- based inhibitors, like clavulanic acid, and are able to hydrolyze several of the most potent ?-lactams in clinical use, the oxyimino cephalosporins and the carbapenems. In part, resistance derives from the structural similarity of the inhibitors to the ?-lactams themselves, both containing a ?-lactam ring. Therefore an urgent need exists for novel inhibitors that do not resemble the ?-lactam substrates. However most structure-based design efforts rely on modification of existing ?-lactam antibiotics. Few attempts have been made to formally map out the binding determinants of a target active site to aid in the discovery of a novel, non-?-lactam inhibitor. This proposal offers a combined approach to formally map the active sites of the class D ?-lactamases, OXA-1 and OXA- 24/40, two highly relevant antibiotic resistance targets. The specific aims of this proposal employ a structure-based consensus overlay approach to identify and characterize the binding sites of OXA-1 and OXA-40. Information from this consensus map of binding sites will be used to discover novel, non-?-lactam inhibitors for these key resistance enzymes using molecular docking. PUBLIC HEALTH RELEVANCE: Currently, antibiotic resistance is one of the most pressing public health crises of the 21st century, and ?-lactamases are the most widespread resistance mechanism to ?-lactam antibiotics. The proposed research is relevant to the mission of the NIH because a better understanding of the structure-function relationship of the class D ?-lactamases OXA-1 and OXA-24/40 will aid in the design and discovery of novel inhibitors for these key targets in bacterial resistance to ?-lactam antibiotics.